How to draw Cumulative Fr.Graph and Find median - Statistics for Civil service

This question was asked in 2011′s GS (Mains) Paper II.

1. Draw an ogive for the following distribution.
2. Read the median from the graph.
3. How many students get between 60 and 72?

Marks	No. of Students
50-55	6
55-60	10
60-65	22
65-70	30
70-75	16
75-80	12
80-100	15

Explanation in this Youtube video:http://www.youtube.com/watch?v=egG3JBTzW3Q